Poultry program's changes aim to stiffen avian flu safeguards

Apr 2, 2009 (CIDRAP News) – The US Department of Agriculture's (USDA's) approval yesterday of two more avian influenza (AI) tests for use in a voluntary national poultry health program will improve the protection of US flocks from avian flu, according to USDA officials and animal health experts.

The two tests will speed the detection of AI in breeding and commercial poultry, the USDA said. The tests are real-time reverse-transcriptase/polymerase chain reaction (RRT-PCR) and type A influenza antigen capture immunoassay.

"The two additional tests can provide highly specific results quickly, making them extremely useful as screening tests for AI and as part of an initial state response and containment plan in the event of an outbreak," the USDA Animal and Plant Health Inspection Service (APHIS) said in a news release.

The approval was among several changes the USDA announced for the National Poultry Improvement Plan (NPIP), a voluntary federal-state-industry program that sets disease-prevention standards for the poultry industry and certifies operations that meet them. One of the other changes is an increase in the minimum frequency of avian flu testing to once every 90 days, instead of 180 days.

Until now, the only two USDA-approved avian flu tests for the NPIP were two serologic tests, according to Dale Lauer, DVM, director of poultry programs at the Minnesota Poultry Testing Laboratory in Willmar, Minn. Serologic tests look for antibodies to the target viruses, whereas the PCR and antigen-capture tests detect actual viral proteins.

"Serology gives you more of a historical perspective; PCR and antigen capture give you more of a real-time perspective," Lauer told CIDRAP News. "This has been used routinely in the live bird markets on the East Coast. They want to know the status of the flocks right now, and that's what these two tests do."

Antigen capture testing yields a result within about an hour, while PCR gives results in about 3 to 5 hours, Lauer said. By comparison, the gold-standard serologic test, called agar gel immunodiffusion, takes 24 to 48 hours, he reported. The other serologic test, ELISA (enzyme-linked immunosorbent assay), can give a result by the end of the day if started in the morning, he said.

The poultry industry has already been using the PCR and antigen-capture tests to some extent, but the USDA seal of approval will encourage broader use, according to Lauer. "With the NPIP you have to have an official test so it's recognized from Minnesota to Maine," he said.

The newly approved tests tell whether an avian flu virus is present, but samples still must be submitted to the USDA National Veterinary Services Laboratory to confirm the subtype, such as H5 or H7, Lauer reported.

As for frequency of testing, most poultry operators already are testing their flocks more often than the new requirement of every 90 days, according to Lauer and David A. Halvorson, DVM, an avian flu expert and veterinarian in avian health at the University of Minnesota in St. Paul.

Halvorson said all chickens and turkeys commercially raised for meat are tested before they are slaughtered. "I think that 90-day testing [rule] is for breeders," he said.

APHIS said the new requirement for 90-day testing "will enhance US flock health and help to maintain the US classification of 'avian influenza clean' for parent egg and meat-type chicken and turkey breeding flocks." The agency is also expanding this classification to include breeding flocks of other birds, such as ostriches and emus.

In addition, APHIS said it is establishing an AI-monitored classification for facilities that slaughter upland game birds and waterfowl, as well as farms that raise those birds for release.

Lauer said that raising game birds and waterfowl for slaughter and for use in hunting preserves is a growing industry: "It's a significant industry here in Minnesota. It probably doesn't get a lot of press, but when you add up the hatcheries, growers, and shooting preserves in the industry, it's significant."

Halvorson said little avian flu activity has been seen in the United States in recent months. There were two low-pathogenic outbreaks in 2008, in Arkansas and Idaho, but, "There haven't been any outbreaks lately that I'm aware of," he said. No outbreaks of the high-pathogenic H5N1 avian flu have been identified in North America to date.

Lauer estimated that about 95% of the poultry industry participates in the NPIP and therefore follows its requirements.